1. Field of the Invention
This invention relates to blood collection and, more particularly, relates to a plastic blood sample collection assembly and method for its manufacture.
2. Background
Blood samples are routinely taken in glass evacuated tubes. One end of a double-ended needle is inserted into a patient's vein. The other end of the needle then punctures a septum covering the open end of the tube so that the vacuum in the tube draws the blood sample through the needle into the tube. Using this technique, a plurality of samples can be taken using a single needle puncture of the skin.
In addition, recent advancements in analytical instrumentation have made it possible to carry out a variety of hematological or chemical diagnostic procedures on very small quantities of blood, such as may be obtained by puncture of a patient's finger, earlobe or an infant's heel. Accordingly, a variety of blood sample microcollection devices have been disclosed in the art.
Plastic tubes have been proposed for blood collection. Plastic offers a number of advantages over glass such as lower breakage, less weight in shipment, and easier disposal by incineration. However, blood does not flow smoothly over hydrophobic surfaces, and blood components, such as platelets, fibrin or clotted blood generally adhere tenaciously to plastic surfaces and hang up on the walls of plastic collection tubes. This is a particular problem in small diameter gravity actuated microcollection tubes during sample collection or in vacuum tubes during subsequent centrifugation. Thus, in any collection apparatus, it is highly advantageous if the collection tube has a surface which resists adherence to blood components at any stage of the collection process or analysis procedure.
Adherence of blood components is not a problem with glass collection tubes, and accordingly, one approach to overcoming this problem in plastic has been to modify the plastic surface to be more glass-like, i.e., to present a hydrophilic surface to the blood. To this end, collection tubes have been treated with a gas plasma to alter the surface chemistry by introduction of heteroatoms. In another, the interior wall surface of the plastic tube has been modified by coating with materials such as surface active agents, water soluble polymers or water insoluble polymers carrying hydrophilic-hydrophobic copolymers.
While the above disclosures have improved blood flow and reduced adherence to plastic blood collection tubes, the problem has not been totally solved because the copolymers on the prior art surfaces are partially or completely removed by the blood so that the surfaces revert back to hydrophobic. There is a need for a collection tube in which adherence is avoided until analysis is complete, and no foreign materials are introduced into the plasma, serum or clot which may interfere with subsequent blood analysis.